The title of Brian Friel's play from 1979 always had a tinge of irony. The decline of a once-prosperous Catholic family, inhabiting a big house on the edge of a Donegal village, was given a Chekhovian tone by Friel, who has frequently adapted the Russian playwright's work. In Patrick Mason's unsentimental new production, the gap between the O'Donnell family's view of themselves and the bleak reality of their lives is heightened. Isolated from the local community but not belonging to the Protestant landowner class, they are caught between two social and political worlds in the 1970s – a position that fascinates a visiting American academic who's researching their cultural environment. This convenient plot device prompts a blend of family reminiscence and fantasy from the visiting son, Casimir.

In Tadhg Murphy's portrayal, Casimir is on the edge of mental stability, with a repertoire of abrupt, jumpy gestures. It is clear that his father, a tyrannical district judge, has inflicted lasting damage on his son, and has possibly driven his wife to suicide. Even bedridden, the patriarch dominates the space by means of an intercom. His youngest daughter, Claire, suffers from depression and her visiting sister, Alice, is a volatile alcoholic. Judith, the unmarried eldest, has given away her child to be raised in an orphanage.

Their political position is complicated by the civil rights upheavals only 30 miles away in Derry, and the sound of gunfire opens the play. Judith is accused by her father of an "enormous betrayal", which could be her pregnancy, her involvement in the demonstrations, or both. While the sisters' roles are sketchily written, their performances – especially by the superb Cathy Belton as Judith – eloquently express unfulfilled lives. The most vocal commentator is Judith's ex-lover, Eamon (Keith McErlean), grandson of the family's housekeeper, who married Alice and is full of class resentment towards them all. Friel is presenting a group portrait, without dramatic resolution, which compacts these dysfunctional layers. One of his least didactic plays, it finishes on a note of indeterminacy, asking how much of this family's plight is inevitable – or whether alternative futures are possible. The strength of this sensitive production is that it leaves that question hanging, offering no easy consolations.